U.S. patent number 6,773,630 [Application Number 10/002,510] was granted by the patent office on 2004-08-10 for process for the gasification of heavy oil.
This patent grant is currently assigned to Texaco Inc.. Invention is credited to Donald D. Brooker, Henry C. Chan, Robert J. Stellaccio.
United States Patent |
6,773,630 |
Stellaccio , et al. |
August 10, 2004 |
Process for the gasification of heavy oil
Abstract
The present invention provides a process whereby a high
viscosity hydrocarbonaceous material is fed to a gasifier for
conversion to synthesis gas. The feedstock, steam, oxygen, and
recycled gasification system water are all fed into the gasifier
through a four stream feed injector. The feedstock in this design
is sandwiched between two oxygen streams so as to provide better
conversion for the exceptionally heavy feed. The fourth stream down
the central bayonet of the feed injector provides the flow path for
the recycled water.
Inventors: |
Stellaccio; Robert J. (Spring,
TX), Brooker; Donald D. (Hopewell Junction, NY), Chan;
Henry C. (Bellaire, TX) |
Assignee: |
Texaco Inc. (San Ramon,
CA)
|
Family
ID: |
21701119 |
Appl.
No.: |
10/002,510 |
Filed: |
November 2, 2001 |
Current U.S.
Class: |
252/373; 48/197R;
48/211; 48/212 |
Current CPC
Class: |
C01B
3/363 (20130101); C01B 2203/0255 (20130101); C01B
2203/1247 (20130101) |
Current International
Class: |
C01B
3/36 (20060101); C01B 3/00 (20060101); C01B
003/24 (); C01B 003/26 () |
Field of
Search: |
;252/373
;48/197R,211,212 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Langel; Wayne A.
Attorney, Agent or Firm: Jones; Josetta I. Howrey, Simon,
Arnold & White, LLP
Claims
What is claimed is:
1. A continuous process for the the partial oxidation of a high
viscosity hydrocarbon feedstream comprising: (1) passing a stream
of water through the central conduit of a four-stream feed injector
mounted in the upper portion of a gasifier, said feed injector
comprising radially spaced concentric central, second, third, and
outer cylindrical conduits, and said conduits being open at their
downstream exit orifices for discharge; (2) simultaneously passing
a high viscosity hydrocarbon feedstream through the third
cylindrical conduit; (3) simultaneously passing a stream of
free-oxygen containing gas, optionally in admixture with a
temperature moderator, through the second and outer cylindrical
conduits; (4) mixing said streams from (1), (2) and (3) together
prior to, at, or downstream from the outer conduit exit orifice;
and (5) reacting the mixture from (4) in the reaction zone of the
gasifier.
2. The process of claim 1 wherein the water is recycled
gasification system water containing carbon soot from the
gasifier.
3. The process of claim 2 wherein the velocity of the water in the
feed injector is about 1.0-120 feet per second.
4. The process of claim 1 wherein the high viscosity hydrocarbon
feedstock is selected from the group consisting of virgin crude,
residua from petroleum distillation and cracking, petroleum
distillate, reduced crude, whole crude, asphalt, coal tar, coal
derived oil, shale oil, tar sand oil, solvent deasphalting bottoms,
and mixtures thereof.
5. The process of claim 4 wherein the high viscosity hydrocarbon
feedstock has a viscosity of about 600 centipoise or greater at a
temperature of 480.degree. F. (249.degree. C.).
6. The process of claim 4 wherein the high viscosity hydrocarbon
feedstock is fed to the gasifier at a temperature between about
550.degree. F. (288.degree. C.) and 600.degree. F. (316.degree.
C.).
7. The process of claim 4 wherein the velocity of the high
viscosity hydrocarbon feedstock in the feed injector is about 10 to
120 feet per second.
8. The process of claim 7 wherein the velocity of the high
viscosity hydrocarbon feedstock is about 25-75 feet per second.
9. The process of claim 1 wherein the free-oxygen containing gas is
selected from the group consisting of air, enriched air, and nearly
pure oxygen.
10. The process of claim 9 wherein the temperature moderator is
either steam, water or an inert gas.
11. The process of claim 9 wherein the velocity of the oxygen
containing gas passing through the first and outer annular passages
is in the range of about 50 feet per second to sonic velocity.
12. The process of claim 11 wherein the velocity of the oxygen
containing gas passing through the first and outer annular passages
is in the range of about 150-750 feet per second.
13. The process of claim 1 wherein the conditions in the reaction
zone of the gasifier are at a temperature between about
1,700.degree. F. (930.degree. C.) and about 3,000.degree. F.
(1650.degree. C.), and a pressure between about 1 atmosphere (100
KPa) and about 250 atmospheres (25,000 KPa).
14. The process of claim 13 wherein the temperature of the gasifier
is between about 2,000.degree. F. (1100.degree. C.) and about
2,800.degree. F. (1540.degree. C.).
15. The process of claim 13 wherein the pressure of the gasifier is
between about about 15 atmospheres (1500 Kpa) and about 150
atmospheres (1500 KPa).
Description
BACKGROUND OF THE INVENTION
The process and advantages of gasifying hydrocarbonaceous material
into synthesis gas are generally known in the industry. In high
temperature gasification processes, synthesis gas is commonly
produced from gaseous combustible fuels, such as natural gas,
liquid combustible fuels, and solid combustible organic fuels, such
as coal, residual petroleum, wood, tar sand, shale oil, and
municipal, agriculture or industrial waste. The gaseous, liquid or
solid combustible organic fuels are reacted with an
oxygen-containing gas, such as air, enriched air, or nearly pure
oxygen, and a temperature modifier, such as steam, in a gasifier to
obtain the synthesis gas.
In the reaction zone of the gasifier, the contents will commonly
reach temperatures in the range of about 1,700.degree. F.
(930.degree. C.) to about 3,000.degree. F. (1650.degree. C.), and
more typically in the range of about 2,000.degree. F. (1100.degree.
C.) to about 2,800.degree. F. (1540.degree. C.). Pressure will
typically be in the range of about 1 atmosphere (100 KPa) to about
250 atmospheres (25,000 KPa), and more typically in the range of
about 15 atmospheres (1500 Kpa) to about 150 atmospheres (1500
KPa).
In a typical gasification process, the synthesis gas will
substantially comprise hydrogen (H.sub.2), carbon monoxide (CO),
and lessor quantities of impurities, such as water (H.sub.2 O),
carbon dioxide (CO.sub.2), carbonyl sulfide (COS), hydrogen sulfide
(H.sub.2 S), nitrogen (N2) and argon (Ar). A quench drum located
below the reaction zone of the gasifier is used to cool the
synthesis gas and remove any solids, particularly ash and/or slag
and the particulate carbon soot leaving the reaction zone of the
gasifier. In the quench drum, the synthesis gas is passed through a
pool of water and exits the quench drum through an outlet nozzle
above the water level. The solid particulates settle in the bottom
of the drum and are removed. Meanwhile, quench water is
continuously removed and added to the quench drum so as to maintain
a steady liquid level in the drum.
The synthesis gas is commonly treated to remove or significantly
reduce the quantity of impurities, particularly H.sub.2 S, COS, and
CO.sub.2 before being used in a downstream process. The synthesis
gas is produced for a variety of useful processes, such as
producing hydrogen for refinement, carbon monoxide for chemicals
production, or producing fuel gas for combustion turbines to
produce electricity.
Generally, the heavier the feed, the higher the carbon to hydrogen
ratio. A high C/H ratio means that the temperature in the reaction
zone of the gasifier will be hotter than when feeds of a lower C/H
ratio are gasified. Thus, the use of a temperature moderator,
usually steam, water or an inert gas such as carbon dioxide, is
required to moderate the temperature in the reaction zone of the
gasifier. Water commonly serves as both the carrier and the
temperature moderator for solid fuels. Water is also commonly mixed
with liquid hydrocarbon fuels. Steam may also be introduced into
the gasifier in admixture with either the feed, the free-oxygen
containing gas stream, or both.
Generally, a portion of the quench water removed from the quench
drum of a gasifier is processed in a downstream unit and recycled
back to be mixed with the feed to the gasifier. In most cases, the
mixing of the quench water and the feed does not cause any
problems. When liquid feedstocks are so heavy that they need to
remain heated so as to keep their viscosities down to pumpable
levels, however, the mixing of the quench water with the feedstocks
is no longer practical.
Viscosity also plays an important part in the conversion of the
feedstock in the gasifier. Generally, it is desirable to atomize
the feed in order to spray fine particles into the reactor. The
finer the particles, the higher the conversion will be. It is
difficult, though, to atomize materials with high viscosities into
fine particles, and the addition of water can produce
non-homogeneous mixtures. Thus, mixing water with a high viscosity
feedstock can also adversely affect conversion in the gasifier if
mixing is poor.
SUMMARY OF THE INVENTION
The present invention provides a process whereby a liquid
hydrocarbonaceous material of high viscosity is fed to a gasifier
for conversion to synthesis gas. The feedstock, steam, oxygen
containing gas, and recycled quench water are all fed into the
gasifier through a four stream feed injector. The feedstock in this
design is sandwiched between two oxygen streams so as to provide
better atomization of the exceptionally heavy feed and, hence,
better conversion to synthesis gas. The central bayonet of the feed
injector provides a flow path for the fourth stream, the quench
water recycle. This arrangement avoids mixing and cooling the
feedstock that would increase the viscosity and thereby lower
conversion in the gasifier.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 provides an overview of a four-stream feed injector for use
in a gasifier.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
The present invention pertains to a novel process for the partial
oxidation, or gasification, of a high viscosity liquid hydrocarbon
feedstock. By definition, gasifier, partial oxidation reactor, or
gasifier are used interchangeably to describe the reactor in which
the partial oxidation of a feedstock takes place, converting the
feedstock into synthesis gas. Partial oxidation reactors are well
known in the art, as are the partial oxidation reaction conditions.
See, for example, U.S. Pat. Nos. 4,328,006, 4,959,080 and
5,281,243, all incorporated herein by reference. The feedstock of a
gasifier is reacted with an oxygen-containing gas, such as air,
enriched air, or nearly pure oxygen, and a temperature modifier,
such as water or steam, in a gasifier to produce the synthesis gas.
The oxygen is used to partially oxidize the carbon in the feedstock
into primarily carbon monoxide and hydrogen gas. The temperature
modifier is used to control the temperature inside the gasifier.
Together, the oxygen and the temperature modifier can impact the
composition of the synthesis gas, but the control of the gasifier
is outside the scope of the present invention.
Partial oxidation reactions use a limited amount of oxygen with
hydrocarbon feedstocks to produce hydrogen and carbon monoxide
(i.e. synthesis gas or syngas), instead of water and carbon dioxide
as occurs in the case of complete oxidation. This reaction is shown
in equation (1) for a straight chain hydrocarbon: ##STR1##
In actuality, this reaction is difficult to carry out as written.
There will always be some production of water and carbon dioxide
via the water gas shift reaction (2): ##STR2##
This reaction is reversible, i.e., the extent to which it proceeds
depends upon the conditions of temperature and pressure. High
temperature and low pressure favor the production of synthesis
gas.
The partial oxidation reaction is conducted under reaction
conditions that are sufficient to convert a desired amount of
carbon-containing feedstock to synthesis gas or syngas. Reaction
temperatures typically range from about 1,700.degree. F.
(930.degree. C.) to about 3,000.degree. F. (1650.degree. C.), and
more typically in the range of about 2,000.degree. F. (1100.degree.
C.) to about 2,800.degree. F. (1540.degree. C.). Pressures
typically range from about 1 atmosphere (100 KPa) to about 250
atmospheres (25,000 KPa), and more typically in the range of about
15 atmospheres (1500 Kpa) to about 150 atmospheres (1500 KPa).
The syngas product composition will vary depending upon the
composition of the feedstock and the reaction conditions. Syngas
generally includes CO, H.sub.2, steam, CO.sub.2, H.sub.2 S, COS,
CH.sub.4, NH.sub.3, N.sub.2, some Ar, and, if present in the feed
to the partial oxidation reactor at high enough concentrations,
less readily oxidizable volatile metals, such as those typically
found in heavy oil fields, such as iron, nickel and vandium.
Ash-containing feedstocks, such as the ones used in the present
invention, frequently produce non-gaseous byproducts that include
coarse slag and other materials, such as char, fine carbon
particles, and inorganic ash. The coarse slag and inorganic ash are
frequently composed of metals such as iron, nickel, sodium,
vanadium, potassium, aluminum, calcium, silicon, and the oxides and
sulfides of these metals.
The coarse slag produced in partial oxidation reactors is commonly
removed from the syngas in molten form from the quench section of a
gasifier. In the quench section of the gasifier, the synthesis gas
product of the gasification reaction is cooled by being passed
through a pool of quench water in a quench chamber immediately
below the gasifier. Slag is cooled and collects in this quench
chamber, from which it and other particulate materials that
accumulate in the quench chamber can be discharged from the
gasification process by use of a lockhopper or other suitable
means. The syngas exiting the quench chamber is passed through an
aqueous scrubber for additional removal of particulates before
further processing. Quench water is continuously removed and added
to the quench chamber so as to maintain a constant level of quench
water in the quench chamber of the gasifier.
In the present invention, a four-stream feed injector for a
gasifier, such as that found in U.S. Pat. No. 4,525,175, is used to
process a high viscosity liquid feedstock. Referring now to FIG. 1,
an illustration of a four stream feed injector tip is provided. The
feed injector 2 includes a central cylindrical conduit 4 and second
6, third 8, and outer 10 cylindrical conduits radially spaced from
each other. This setup provides a center passage 12, and a first
14, a second 16, and an outer 18 annular coaxial concentric annular
passage. The conduits are coaxial with the central longitudinal
axis of the feed injector. All of the conduits and annular passages
are closed at the upstream ends and open at the downstream ends.
The upstream ends of each conduit have a flanged inlet nozzle 20
for the introduction of material. The inside and outside diameters
of the central conduit are reduced near the downstream end of the
feed injector to form a conical shaped nozzle. This is generally
representative of a four-stream feed injector that can be employed
for use in the present invention. It is within the scope of this
invention to use any four-stream feed injector for use in the
partial oxidation of a high viscosity feedstock.
The feed injector assembly is inserted downward through a top inlet
port of a gasifier, for example as shown in U.S. Pat. No.
3,544,291. The feed injector extends along the central longitudinal
axis of the gasifier with the downstream end discharging directly
into the reaction zone. The relative proportions of the reactant
feedstreams introduced into the gasifier are carfully regulated to
convert a substantial portion of the carbon in the fuel e.g., up to
about 90% or more by weight, to carbon oxides; and to maintain an
autogenous reaction zone temperature in the range of 1,700.degree.
F. (930.degree. C.) to about 3,000.degree. F. (1650.degree. C.),
and more typically in the range of about 2,000.degree. F.
(1100.degree. C.) to about 2,800.degree. F. (1540.degree. C.).
The reactants that are to be introduced into the four-stream feed
injector assembly are a oxygen-containing gas, such as air,
enriched air, or nearly pure oxygen, a temperature modifier, such
as steam and/or water, preferably recycled water from the
gasification system, and the high viscosity liquid hydrocarbon
feedstock. The oxygen-containing gas, optionally admixed with steam
or boiler feed water, is directed into the second 6 and outer 10
conduits of the feed injector, i.e. the first 14 and outer 18
annular coaxial concentric annular passages. The high viscosity
liquid hydrocarbon feedstock is to be introduced into the feed
injector through the third conduit 8 of the feed injector, i.e. the
second 16 annular coaxial concentric annular passage. A water
temperature modifier, preferably recycled gasification system water
containing carbon soot from the gasifier, is fed through the center
cylindrical conduit 4 of the feed injector into the center passage
12 of the injector.
By definition, a high viscosity liquid hydrocarbon is any one of a
number of heavy oils known in the industry. The group of known
heavy oils consists, among others, of virgin crude, residua from
petroleum distillation and cracking, petroleum distillate, reduced
crude, whole crude, asphalt, coal tar, coal derived oil, shale oil,
tar sand oil, solvent deasphalting bottoms, and mixtures thereof.
Generally, these heavy oils have high sulfur and nitrogen component
concentrations, and they usually contain a high concentration of
nickel, iron, and vanadium-containing ash. Some feeds may also
contain catalyst fines consisting of silicon and alumina materials.
The feedstocks of the present invention are sometimes referred to
as "bottom of the barrel" hydrocarbons, named so because of their
propensity to be the thickest, heaviest components of refined crude
oil.
The ash in the feed consists of nickel, iron, and vanadium, as well
as catalyst fines (such as those from a fluid catalytic cracking
unit (FCCU), from previous processing operations). The combination
of these components produces an ash that will eventually plug the
gasifier with a coarse, viscous slag that does not readily flow out
of the gasifier into the quench drum during normal operation.
Commonly, the ash-containing feedstocks used in the present
invention are mixed with a fluxing agent prior to introduction into
the gasifier. The fluxing agent is required to promote fluidity of
the ash in the feed during gasification. It provides additional
components that alter the slag fluid behavior so that the slag
flows out of the gasifier during normal operation. The fluxing
agent is usually prepared from a blend of calcium oxide and FCCU
catalyst fines, and it is introduced into the feedstock as a liquid
slurry with a carrying agent (preferably one that can also act as a
cutter stock and further reduce the viscosity of the feedstock,
cush as FCC decant oil).
All the feedstocks of the present invention share in common a high
viscosity that requires heating to keep the feedstock at a suitable
viscosity for pumping. For example, a normal, low viscosity vacuum
resid feed to a gasifier is commonly heated to 480.degree. F. prior
to introduction to the feed injector. The viscosity of this feed at
this temperature is preferably 20 centipoise or less, well below
the limit for adequate pumping. The high viscosity feedstock of the
present invention generally has a viscosity of 600 centipoise or
greater at the normal feed temperature of about 480.degree. F.
(249.degree. C.). The high viscosity feedstock would need to be
heated using an auxiliary heat transfer medium, such as
DOWTHERM.TM., to a temperature range of about 550-600.degree. F.
(288-316.degree. C.) in order to keep its viscosity down to
adequately pump the feedstock and to atomize the feedstock in the
feed injector. The velocity of the stream of the high viscosity
liquid hydrocarbon feedstock passing through the third conduit of
the feed injector (the second annular passage of the burner) is in
the range of about 1.0-100 feed per second, preferably about 25-75
feet per second.
Because of the high viscosity feedstock that the present invention
is designed to handle, the water modifier cannot be mixed with the
feedstock prior to its introduction into the gasifier. Inclusion of
the water modifier with the high viscosity feedstock would decrease
the temperature of the feedstock, thus increasing the viscosity and
hindering the processing of the high viscosity feedstock. The water
is still injected into the gasifier, but is done separately from
the feedstock so as to avoid cooling the feedstock. This is why the
present invention proposes to feed the water moderator through the
center conduit of the four-stream feed injector. The velocity of
the water moderator through the center conduit of the four-stream
feed injector is in the range of about 10-120 feet per second,
preferably 20-60 feet per second.
The oxygen-containing gas, optionally admixed with steam as an
additional temperature modifier, is directed into the second and
outer conduits of the burner, i.e. the first and outer annular
coaxial concentric annular passages. The oxygen-containing gas is
fed on either side of the high viscosity liquid hydrocarbon
feedstock, which is introduced into the burner through the third
conduit of the burner, i.e. the second annular coaxial concentric
annular passages. This allows the oxygen-containing gas streams to
provide shearing of the annular hydrocarbon feedstock stream to
thereby provide some atomization of the feedstock stream. The
velocity of the oxygen-containing gas streams (with or without
admixture with steam as a temperature moderator) passing through
the first and outer annular passages of the four-stream burner is
in the range of about 50 feet per second to sonic velocity,
preferably about 150-750 feet per second.
The use of a four-stream feed injector is imperative in the present
invention. The configuration of sandwiching the hydrocarbon stream
between the two oxygen streams provides better conversion with
these heavy feeds by providing for increased atomization and better
mixing of the feedstock with the oxygen containing gas. Sending
water, preferably recycled soot containing water, down the central
conduit of the feed injector allows the feedstock to stay hot and
avoids mixing and cooling of the feedstock with water that could
decrease viscosity and lower conversion.
In view of the above disclosure, one of ordinary skill in the art
should appreciate that the present invention includes a continuous
process for the the partial oxidation of a high viscosity
hydrocarbon feedstream comprising passing a stream of water through
the central conduit of a four-stream feed injector mounted in the
upper portion of a gasifier, said feed injector comprising radially
spaced concentric central, second, third, and outer cylindrical
conduits, said conduits being open at their downstream exit orifice
for discharge; simultaneously passing a high viscosity hydrocarbon
feedstream through the third cylindrical conduit; simultaneously
passing a stream of free-oxygen containing gas, optionally in
admixture with a temperature moderator, through the second and
outer cylindrical conduits; mixing the above mentioned streams
together prior to, at, or downstream from the outer conduit exit
orifices; and reacting the mixture in the reaction zone of the
gasifier.
In a preferred embodiment, the water used is recycled gasification
system water containing carbon soot from the gasifier traveling at
a velocity of about 1.0-100 feet per second. The high viscosity
hydrocarbon feedstock is selected from the group consisting of
virgin crude, residua from petroleum distillation and cracking,
petroleum distillate, reduced crude, whole crude, asphalt, coal
tar, coal derived oil, shale oil, tar sand oil, solvent
deasphalting bottoms, and mixtures thereof. High viscosity
hydrocarbon feedstock generally has a viscosity of 600 centipoise
or greater at a temperature of 480.degree. F. (249.degree. C.). It
is fed to the feed injector at a temperature between about
550.degree. F. (288.degree. C.) and 600.degree. F. (316.degree. C.)
and travels through the feed injector at a velocity of about 10 to
100 feet per second, preferably at about 25-75 feet per second.
Free-oxygen containing gas is selected from the group consisting of
air, enriched air, and nearly pure oxygen, optionally admixed with
steam, water or an inert gas as the temperature moderator. The
velocity of the oxygen containing gas passing through the first and
outer annular passages of the feed injector is generally in the
range of 50 feet per second to sonic velocity, preferably in the
range of about 150-750 feet per second.
The reaction zone of the gasifier is usually at a temperature
between about 1,700.degree. F. (930.degree. C.) and about
3,000.degree. F. (1650.degree. C.), preferably at a temperature
between about 2,000.degree. F. (1100.degree. C.) and about
2,800.degree. F. (1540.degree. C.). The gasification pressure is
usually between about 1 atmosphere (100 KPa) and about 250
atmospheres (25,000 KPa), preferably between about about 15
atmospheres (1500 Kpa) and about 150 atmospheres (1500 KPa).
While the methods of this invention have been described in terms of
preferred embodiments, it will be apparent to those of skill in the
art that variations may be applied to the process described herein
without departing from the concept and scope of the invention. All
such similar substitutes and modifications apparent to those
skilled in the art are deemed to be within the scope and concept of
the invention as it is set out in the following claims.
* * * * *